From German Patent DE 43 16 542 C1, a bone screw is known with which a longitudinally grooved rod can be fixed in a manner secure against relative rotation. To that end, the bone screw has a bifurcated head, in whose groove the longitudinally grooved rod can be placed. The grooved bottom is itself provided with longitudinal grooves, which establish a positive connection with the rod. For fixing the rod, a cap nut is screwed onto the bifurcated head, and the rod is firmly clamped in the groove bottom with this nut. Because the rod is fixed to the bone screw in a manner secured against relative rotation, high correction forces or retention forces can be transmitted. However, to transmit forces oriented in the longitudinal direction of the rod, additional aids or additional rods are needed.
From German Patent DE 26 49 942 C2, a corrective implant is known in which such longitudinal forces can be introduced optimally into the bone screws via a threaded rod. Once again, the bone screw has a bifurcated head, in which the threaded rod is placed. The fixation of the threaded rod is done by means of two nuts, which are seated on the threaded rod and are screwed laterally partway into the bifurcated head. In this way, the threaded rod is fixed on the bone screw. It has proved to be a disadvantage in this known construction that fastening the threaded rod to the bifurcated head of the bone screw, and in particular screwing the nuts into the bifurcated head, is inconvenient and wastes time, since the nuts can be turned or tightened only with an engineer's wrench, and displacement of the threaded rod is possible only whenever the nut is spaced sufficiently far from the bifurcated head.